Thread: 1932 ford disc brakes locking up

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Originally Posted by Bob o

I can the push rod is adjustable. There is a tiny bit of play I will adjust the play out of the push rod it might have 1/16 or a bit more of slack right now

If it only has 1/16" of play how did the rod come out of the cup? You need about 1/16" of play between the piston cup and the rod end to ensure that the piston comes back to let the pressure bleed back. Something sounds strange.....

Roger is right, ya need about 1/16 play, as I said B4 put a return spring on it and be done with it !!!!!!

Originally Posted by DA34GUY

Roger is right, ya need about 1/16 play, as I said B4 put a return spring on it and be done with it !!!!!!

What I don't understand is how a guy could get the rod to come out of the cup in the back side of the piston with only 1/16" of play, given the strong internal spring in the MC pushing the piston spool back against the rod. I suppose the answer may be that when the new MC was installed the rod was off center, depressing the piston about 3/8", and wasn't noticed? If you didn't disconnect the rod from the pedal it wouldn't be that hard to do, and it's about the only thing that makes sense to me. If that's the case I'd say it's fixed.

I guess no one looked at the pic that comes up in the link I posted showing the back of two different mastercylinders with the different holes for seating the push rod----------this is an common issue of older cars, brake conversions and the MODERN auto parts store dealing with inexperienced people----------I would like to do a thread on brakes and master cylinders but have been advised not to expose myself to the liability of some one coming back and sueing me because they had an accident and had used the thread as a guide for doing there brakes-----------so I guess that I'll check out of this'un because he doesn't seem to want to follow much od any ones advise------

Originally Posted by DA34GUY

Roger is right, ya need about 1/16 play, as I said B4 put a return spring on it and be done with it !!!!!!

The return spring would actually make it worse it would return the brake pedal one it's own without any help from the mastercylinder. Thus causing the pushrod to become disengaged whit the piston. I going to keep an eye on it and if if it comes out again I will add a support for the pushrod so it can't come out

Bobo


You need a support/stop for the pedal somewhere so the spring can pull the pedal back to the same spot all the time---THEN ADJUST for the 1/16 or so clearance where the push rod seats against the piston in the master--------


Does your master have the shallow or deep recess for the push rod??????????


When swapping master cyls, there are at least two different length master cyl push rods coming OUT of the booster. To fit different depth master cyls. The rod can be removed from the booster by pulling on it. It has an O ring on it. If the master cyl you get is deeper where the pushrod goes, you either have to swap the pushrod, or you can cut a length of rod or bolt and put it inside the master cyl to make it the same as the shorter drum brake master cyl. If the rod is too long you can cut it.
UNDER NO CIRCUMSTANCES USE A SHORT DEPTH MASTER ON A MANUAL SYSTEM. THE PUSHROD CAN FALL OUT AND YOU WILL HAVE NO BRAKES!

If the push rod is the wrong length, your brakes will lock or not work at all!

Jerry. The master cylinder is a model #10-1521 it's for mid 70's Chevy passenger cars. The hole for the push rod is about 3/8 deep. Not sure if that's considered shallow or not??? The brake pedal has a stop just nothing supporting the push rod. My plan is to fab up a small sleeve for the push rod to ride thru so it can't pop out?? What do you think?

you need a master with that deeper hole for the rod and a longer rod--- your problem is that the rod /pedal comes back faster that the master cylinder and falls out of the center which then doesn't let the sleeve uncover the port keeping pressure on the brakes---


if you look at the pic of the two masters in the link I posted you should be able to visualize

I'm thinking that the mid 70's master should have a heavy rubber o-ring or bushing that the rod pushes into to keep it centered and secure. If it was for a manual (non power assist) braking system. I've changed many that you had to literally use both hands and with your chest across the wheel, and a mighty heave ho to rip the rod from the master. Some used a metal clip with "fingers" to latch onto the rod and others used a rubber or plastic o-ring/bushing to hold onto the rod. Again, this is only for manual masters..See if you can't look up inside the master bore and tell if there is a rubber / plastic piece in there or a circle clip of fingers? Or maybe a place for them??

Yep that is my thinking also-----I bet he has a master for power brakes------


Last build that I did without making sure all that stuff was right was my Monza Pro stocker back in late 70s----brake pedal came back on the launch and pulled rod out off master bore---luckily it was the first licensing pass and was a short launch/run-------

Originally Posted by jerry clayton

Last build that I did without making sure all that stuff was right was my Monza Pro stocker back in late 70s----brake pedal came back on the launch and pulled rod out off master bore---luckily it was the first licensing pass and was a short launch/run-------

I'll bet a wardrobe change was in order shortly after!!!

Well no wardrobe change as I only sorta just left starting line, pulled second and shut down (NHRA license runs), however we had a borrowed trailer and on the way home the winch cable (which was severely frayed) broke and the car came off the trailer and then ran off the road side down a sloping exit rampway grassy area before hitting a cyclone fence head on---------every time that car was damaged there wasn't anyone in it!!!!!!!!!!!

That musta made for a long day! I can't say I ever lost a car off a trailer... good thing it didn't hit another car!!!